On 20/05/2021 11:09, Marc Zyngier wrote:
> On Wed, 19 May 2021 14:26:31 +0100,
> Steven Price <steven.price@xxxxxxx> wrote:
>>
>> On 17/05/2021 18:40, Marc Zyngier wrote:
>>> On Mon, 17 May 2021 13:32:37 +0100,
>>> Steven Price <steven.price@xxxxxxx> wrote:
>>>>
>>>> It's now safe for the VMM to enable MTE in a guest, so expose the
>>>> capability to user space.
>>>>
>>>> Signed-off-by: Steven Price <steven.price@xxxxxxx>
>>>> ---
>>>> arch/arm64/kvm/arm.c | 9 +++++++++
>>>> arch/arm64/kvm/sys_regs.c | 3 +++
>>>> 2 files changed, 12 insertions(+)
>>>>
>>>> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
>>>> index 1cb39c0803a4..e89a5e275e25 100644
>>>> --- a/arch/arm64/kvm/arm.c
>>>> +++ b/arch/arm64/kvm/arm.c
>>>> @@ -93,6 +93,12 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
>>>> r = 0;
>>>> kvm->arch.return_nisv_io_abort_to_user = true;
>>>> break;
>>>> + case KVM_CAP_ARM_MTE:
>>>> + if (!system_supports_mte() || kvm->created_vcpus)
>>>> + return -EINVAL;
>>>> + r = 0;
>>>> + kvm->arch.mte_enabled = true;
>>>
>>> As far as I can tell from the architecture, this isn't valid for a
>>> 32bit guest.
>>
>> Indeed, however the MTE flag is a property of the VM not of the vCPU.
>> And, unless I'm mistaken, it's technically possible to create a VM where
>> some CPUs are 32 bit and some 64 bit. Not that I can see much use of a
>> configuration like that.
>
> It looks that this is indeed a bug, and I'm on my way to squash it.
> Can't believe we allowed that for so long...
Ah, well if you're going to kill off mixed 32bit/64bit VMs then...
> But the architecture clearly states:
>
> <quote>
> These features are supported in AArch64 state only.
> </quote>
>
> So I'd expect something like:
>
> diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
> index 956cdc240148..50635eacfa43 100644
> --- a/arch/arm64/kvm/reset.c
> +++ b/arch/arm64/kvm/reset.c
> @@ -220,7 +220,8 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
> switch (vcpu->arch.target) {
> default:
> if (test_bit(KVM_ARM_VCPU_EL1_32BIT, vcpu->arch.features)) {
> - if (!cpus_have_const_cap(ARM64_HAS_32BIT_EL1)) {
> + if (!cpus_have_const_cap(ARM64_HAS_32BIT_EL1) ||
> + vcpu->kvm->arch.mte_enabled) {
> ret = -EINVAL;
> goto out;
> }
>
> that makes it completely impossible to create 32bit CPUs within a
> MTE-enabled guest.
... that makes complete sense, and I'll include this hunk in my next
posting.
Thanks,
Steve
_______________________________________________
kvmarm mailing list
kvmarm@xxxxxxxxxxxxxxxxxxxxx
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
